As is known in the art, current cellular telephone use has expanded rapidly over the past few years. While typically a user subscribes to only one service provider and is assigned a single telephone number, many subscribers have cellular phones adapted to operate with two different telephone numbers. Thus, when the subscriber operates in one geographical location he/she manually selects one of two Number Assignment Modules (NAMs) provided within his/her cellular telephone. In this way, if the subscriber generally travels to, and works in, two geographical locations he/she can select the NAM associated with a local service provider thereby reducing long distance telephone costs and inter-network roaming charges. Thus, these users are able to obtain two subscriptions from two service providers in two different geographical locations for the same handset. In other words, dual subscription is achieved by having the same handset programmed with different telephone numbers of subscription information in different Number Assignment Modules (NAMs); one for each of the two different geographical locations of the local service provider. This arrangement allows a roaming subscriber to save roaming fees and long distance charges, which can be very expensive if the user frequently travels between two locations and merely uses the same subscribed local service provider when on travel. However, as noted above, the user must manually select the NAM to be used and the NAMs are not removable by the user.
As is also known in the art, certain cellular telephones are adapted to receive a credit-card sized Subscriber Identity Module (SIM). Each SIM is associated with a unique service provider and has stored therein different subscriber information. This information is transmitted to a receiving radio base station cell to obtain network access. Thus, in one example, one SIM may be associated with a subscriber's business telephone number and another with his/her home telephone number. In this case, each SIM may be for the same or different providers in the same Public Land Mobile Network (PLMN), or for the same or different providers in different PLMNs. Thus, if a subscriber is on travel to a different geographical location from his/her home office, he/she needs only to remove the SIM from his/her handset, slips it into his/her wallet, rents a handset at the other location where the radio frequency coverage is different from his/her own handset (i.e, where the user travels from the United States to Europe) and merely inserts the SIM into the rented handset. During operation, the subscriber's information is transmitted from the SIM to the local base station cell to obtain authorization from the home PLMN.
In a PCS 1900 network, multiple subscriber number service for voice application is not possible with a single Subscriber Identity Module (SIM) in the handset since it can only be provided with one Mobile Subscriber Integrated Service Digital Network (MSISDN) number for voice service per Global System for Mobile (GSM) standards. In GSM communication, standards allow for two SIMs in a handset. One of the SIMs must be the plug-in type. The plug-in type SIM is very small (i.e., chip size) and, if removed from the handset, may be easily lost. For the GSM handset, there can only be one full size, i.e., credit-card like SIM.
It is noted that both NAM and SIM refer to modules which provide subscriber identification information and are both sometimes referred to hereinafter as subscriber identity modules.